I found this price book, whilst looking for something else, in a cupboard under a bookcase
I was looking through it, at the SVO prices
Look at the price for vacuum, & air, brakes for towing
That raises the braked limit from 3500kg to 4000kg, for specialist useage
A 130 'double-cab' pick-up, the most likely vehicle to be fitted such is listed at £24,995 (inc VAT)
As seen
'here